Pneumatic fluid weighing device

ABSTRACT

An apparatus for weighing drilling fluid being pumped into a well and for weighing the drilling fluid returning from the well during drilling operations. A pair of pneumatic conduits are connected in parallel relationship with their one ends communicating with a source of air under pressure for bubbling a constant supply of air through the tubes. The other ends of the conduits are open and are spaced from each other a distance of 8.35 inches. When used to weigh the drilling fluid being pumped into the well a float device is connected to the tubes for floating the tubes in vertical position in a drilling fluid suction tank. When used to weigh drilling fluid returning from the well a housing having an outlet opening in the bottom portion thereof surrounds the conduits and is connected on the outside of a shaker box and receives drilling fluid from the shaker box through an opening in the shaker box which communicates with an opening in the housing. A differential pressure recording device is connected between the pneumatic tubes and the air source.

United States Patent [191 Rochon et al.

[ Oct. 14, 1975 PNEUMATIC FLUID WEIGHING DEVICE [76] Inventors: RobertW. Rochon, 4436 Blanco Road, San Antonio, Tex. 78212; Joseph W. Sneed,Jr., 5706 Ben Casey, San Antonio, Tex. 78240 22 Filed: May 14, 1974 211App]. No.: 469,876

Related US. Application Data [63] Continuation of Ser. No. 324,099, Jan.16, 1973,

Primary Examiner.lerry W. Myracle Attorney, Agent, or FirmCox, Smith,Smith, Hale & Guenther Incorporated ABSTRACT An apparatus for weighingdrilling fluid being pumped into a well and for weighing the drillingfluid returning from the well during drilling operations. A pair ofpneumatic conduits are connected in parallel relationship with their oneends communicating with a source of air under pressure for bubbling aconstant supply of air through the tubes. The other ends of the conduitsare open and are spaced from each other a distance of 8.35 inches. Whenused to weigh the drilling fluid being pumped into the well a floatdevice is connected to the tubes for floating the tubes in verticalposition in a drilling fluid suction tank. When used to weigh drillingfluid returning from the well a housing having an outlet opening in thebottom portion thereof surrounds the conduits and is connected on theoutside of a shaker box and receives drilling fluid from the shaker boxthrough an opening in the shaker box which communicates with an openingin the housing. A differential pressure recording device is connectedbetween the pneumatic tubes and the air source.

6 Claims, 4 Drawing Figures U.S. Patent Oct. 14, 1975 Sheet 1 of23,911,741

FIG. 2

U.S.P1tent Oct. 4,1975 816612012 3,911,741

FIG.3

FIG. 4

PNEUMATIC FLUID WEIGI-IING DEVICE This application is a continuation ofUS. Pat. application Ser. No. 324,099 filed on Jan. 16, 1973, expresslyabandoned upon filing this application.

BACKGROUND OF THE INVENTION This invention relates to an apparatus foraccurately determining the unit weight of drilling fluid being pumpedinto a well during drilling operations and for determining the weight ofthe drilling fluid returning from the well during drilling operations.

During the drilling of a well in the quest for hydrocarbons using therotary method of drilling, it is necessary to pump or circulate adrilling fluid, known in the art as drilling mud downwardly through thedrill pipe to which the drill bit is attached and outwardly through thedrill bit into the annulus formed by the drill pipe and the wall of thewell bore for return upwardly through the annulus to the surface.

A container known as a suction tank contains the drilling fluid forpumping through the drill pipe into the well. The circulating drillingmud exits from the drill bit returning to the surface through theannulus between the drill pipe and the wall of the well bore and outinto a shaker box where the cuttings which are drilled up are separatedfrom the returning drilling fluid. The drilling fluid then flows fromthe shaker box via a settling tank back to the suction tank for returnto the well. The drilling mud is essential to a well drilling operationas it serves to carry away the cuttings from the drill bit to facilitatedrilling and act as a medium for transporting the cuttings from thedrill bit area out of the well bore to be separated from the mud viashaker or settled out in a mud pit at the top of the well prior torecirculation. The primary function of the drilling mud is to act as astopper in the well by exerting hydrostatic pressure on the bottom ofthe well according to the specific weight of the drilling mud thereaboveto balance or overcome the formation pressure in order to preventblowouts. The pressure of the formation adjacent the drill bit, orbottom-hole pressure must also be taken into consideration because thispressure must be sufficient to sustain the hydrostatic pressure of themud in order to prevent loss of circulation, that is the loss of the mudas it escapes into the formation due to the pressure exerted by the mudcolumn being substantially greater than the formation pressure itself.It is therefore essential that the pressures in the well bore, i.e. theformation pressure and the hydrostatic pressure of the drilling mud bemaintained near balanced condition. The drilling mud also acts as asealing means on the well bore by caking on the surface of the bore toseal the bore and prevent the drilling mud from flowing out into porousformation material.

It is necessary that the drilling mud must be of sufficient weight tobalance against the force of any upwardly acting hydrostatic pressuresuch as the pressure of gas, water, or oil which may be exposed indrilling and at the same time the drilling mud should not become soheavy that it enters the formation causing a loss of circulation. Asconditions vary in the course of 'drilling, the weight of the drillingmud has to be varied constantly to meet these changing conditions. Forinstance, if the gas sand is penetrated the gas in the bore space willbecome a part of the drilling fluid. As the fluids are pumped out of thehole the gas expands, mud flows out of the hole at a faster rate than itenters and the mud weight becomes considerably lighter. Such a conditionmust be detected immediately as remedial action may be necessary by theaddition of weight material to the drilling fluid otherwise the fluidmight not contain the forces of the formation pressures reactingupwardly thereagainst with the consequence that a blowout may occur.

The use of excessive ,mud weight to provide a large factor of safetyagainst blowouts was previously used as a standard drilling procedure.Of course, as mentioned previously, such an overbalance may result in aloss of circulation where the formation pressures are incapable ofwithstanding the over-balanced hydrostatic pressures of the drillingmud. For reasons of economy, a new drilling concept of balanced pressuredrilling was adopted and it became essential that continual accuratemeasurement of the mud weight be maintained at all times during thedrilling operation. Balanced drilling grew out of the need for moreeconomy in the drilling operation, since less dense drilling mud allowsfaster drilling with less wear on the equipment. Since balanced pressuredrilling reduced the factor of safety against blowouts which resultedfrom excess mud weight it becomes imperative that accurate andcontinuous mud weights into and out of the well be logged since the bestevaluation of bottom hole conditions is to continuously determine theabsence or to accurately measure the volume of gas entering the hole.Such a determination will provide information essential to maintainingminimum mud weight to balance the bottom hole pressures and preventblowout conditions.

Mud weight, the key to well safety, is the most valuable information onthe drilling well yet it has been the most neglected. There has neverbeen a problem of knowing when there was a lot of gas since it could bedetected by smelling, tasting and visual observation and the developmentof gas detecting equipment was directed to the identification of thesub-sensory or small amounts of gas. No appreciable progress was made inthe measurement of large quantities of gas and the standard practice ofchecking mud weights today is the use of the hand balance device forperiodic checks. Several types of continuous mud weighing devices havebeen developed, however, due to their limitations, it is estimated thatonly one well out of a hundred has a continuous mud weight device. Theprior devices have consisted of mechanical and float devices with movingparts and pressure differential devices. Both the measurement of the mudweight in at the suction tank and the mud weight out of the shaker boxhas had its problems. The use of pneumatic tubes in the shaker box wereaffected by the excessive turbulence of the mud flowing into the shakerbox and the box would fill with cuttings and stop up the tubes. In thesuction tank on the mud discharge side, excessive changes in the levelof the mud in the tank would leave the permanently placed pneumatictubes out of the mud. Problems were also compounded by changes insubmersion depths which affected the other properties of the mud such asthe viscosity and gell strength.

It is recognized that a continuous accurate measure of the amount of gasentering the formation is valuable information for properly balancing awell during the drilling operation. Drilling for hydrocarbons ishazardous as evidenced by frequent blowouts which cause considerable airand water pollution and general ecological damage. Blowouts result fromthe unknown relationship between f; nation pressures and the weight ofthe drilling mud which is predetermined for formation pressurecontainment and penetration control. The mud weight determinations areinitially based on historical data for a particular formation which ofcourse is only an approximation and it is therefore essential thataccurate and continuous determinations be made of the drilling fluidexiting from a well since the mud weight out of the well is a reflectionof the bottom hole pressure relationship and the content of theformation being drilled up.

Many devices have been developed to give advace warning of potentialtrouble in the drilling of a well so that remedial action may be takento minimize the trouble and control the well. The basic warning andindication of trouble is the relationship between the input drilling mudand the output drilling mud, i.e. the weight per unit volume and thevolume per unit time of the mud at the entrance and at the exit from thewell. If the volume of the returning drilling fluid is less than that ofthe input drilling fluid, the formation is taking the drilling fluidswhich is commonly referred to as a loss of circulation wherein thedrilling mud enters the forma tion faster than it is pumped into thewell. The sooner this condition is determined, the easier it is to sealoff the zones that are taking the fluids. If more mud comes out of thehole than is pumped in, formation fluids such as salt water, gas or oilare entering the bore hole. When fluids enter the bore hole, mudcontaining pressures are inadequate since the fluid entering the holewill mix with the drilling mud being pumped into the well and lightenthe weight of the mud column of the mixture being pumped out of thewell. To make an accurate determination of the gas entering theformation, a new U-tube detector was invented for accurately andcontinuously measuring large quantities of gas entering the formation.This device, which measured the weight of the mud returning from thewell bore prior to gas aeration at atmospheric pressure was difficult toset up and maintain.

SUMMARY OF THE INVENTION The present invention consists of an apparatusfor accurately measuring the weight of the drilling mud being pumpedinto the well and accurately determining the weight of the mud beingpumped out of the well and continuously logging the information on atime chart so that an accurate determination can be made as to changesin the mud weight resulting from bottom hole conditions. Thedeterminations of mud weight in and mud weight out require twomeasurements, one of which is made on the suction tank which containsthe drilling fluid being pumped into the well and the other measurementis made on the shaker box which contains the drilling fluids returningfrom the well. The basic apparatus for making both determinations isessentially the same except for slight modifications in its arrangementon the suction tank and shaker box, respectively. The apparatus of thisinvention consists of a pressure differential densiometer in which theweight of the fluid is measured by the difference in pressure betweentwo pneumatic tubes submerged in the drilling fluid, both tubes havingan independently controlled air supply. The pressure of the air in eachtube is regulated to the same rate and the flow is metered so that bothtubes have the same volume of air at equal pressure flowing into the mudbeing measured. The air outlet ends of the tubes are positioned atexactly 8.35 inches apart which represents the weight of water in poundsper gallons. Therefore when the weight of the drilling fluid isincreased or decreased the pressure differential at the ends of thesubmerged tubes will increase or decrease by 1 inch of water pressurefor each pound per gallon increase or decrease in the weight of thedrilling fluid. This permits direct reading in pounds per gallon on apressure differential recording device.

Prior attempts to use pressure differential pneumatic tubes formeasuring the weight of fluid returning from the well have not beensuccessful because of the shaker box turbulence and plugging tubes withthe cuttings being returned from the well.

It is an object of this invention to solve the problems previouslyencountered with the use of pressure differential tubes on the shakerbox by enclosing the tubes in a housing and mounting the housing on theoutside of the shaker box. The housing communicates through an openingin the side of the housing with the interior of the shaker box via anopening in the wall of the shaker box and a restricted discharge openingin the bottom of the housinginsures that the housing will remain full ofdrilling fluid thereby insuring accurate weight determinationsregardless of the turbulence inside the shaker box itself. This alsoeliminates the problem of tube plugging from the cuttings since thecuttings are excluded from the tube housing.

The use of pressure differential tubes on the suction tank fordetermining the weight of mud being pumped into the well has encounteredmany difficulties also. Excessive changes of the level of the drillingfluid in the suction tank oftentimes leaves pneumatic tubes permanentlypositioned in the tank completely out of the drilling fluid and therebyfailing to record the drilling mud weight. Fluctuations in the level ofthe drilling fluid in the suction tank causes substantial changes in thesubmersion depth of the pneumatic tubes. This results in error in therecorded mud weights due to changes in mud viscosity and gell strengthwhich vary with mud depth.

It is a further object of this invention to provide a means whereby thepneumatic tubes will be maintained at a constant submersion depth in thesuction tank regardless of variations in the level of the drilling fluidin the tank.

Other and further objects and advantages of the pres ent invention willbecome apparent from the detailed description of the preferredembodiment.

BRIEF DESCRlPTlON OF THE DRAWINGS FIG. 1 is a schematic sectional viewof a drilling rig including pumps, well bore, suction tank and shakerbox' with the present invention included therein.

FIG. 2 is a schematic partial section view disclosing the specificarrangement of the pneumatic tubes connected to the air supply means andrecording device.

FIG. 3 is a vertical section view of the apparatus of this invention asmodified for use on the shaker box for weighing drilling fluid returningfrom the well.

FIG. 4 is a perspective view partly in section, of the apparatus of thisinvention mounted in the suction tank and modified for use in weighingdrilling fluid being pumped into the well.

DESCRIPTION OF THE PREFERRED EMBODIMENT As can be seen from FIG. 1, aderrick 2 has been illustrated as mounted over the well bore 3 which isbeing drilled by the drill bit 4 connected to drill pipe 5 which is inturn connected to a swivel 6, a travelling block 7 and the hoistinglines 8. This drill pipe is rotated by rotary table 9 which receives itspower from a suitable source. The well bore 3 as indicated is beingfilled with a drilling mud 10 which is forced downwardly by pump 12through a hose 14 and into the upper end of the drill pipe 5. The mud ispicked up by the pump 12 from the suction tank 21 via conduit 22 shownpartly in schematic form in FIG. 1. Well casing 11 exits from the bore 3in known manner and has a blowout preventer 23 mounted on top of saidcasing with a bell nipple 24 mounted on top of the blowout preventer 23.The drilling mud circulates upwardly in the casing within the annularspace between the casing 11 and the drill pipe 5 and will rise to alevel such as in the casing depending upon the rate of circulation whichis being maintained by the pump 12. The discharge flowline 16 allows thedrilling mud to discharge from the well bore and into the shaker box 17.The drilling mud exits from the shaker box over a vibrating screen 19and into settling tank 25. The drilling fluid then travels from thesettling tank 25 via conduit 26 and into the suction tank 21 to berecycled into the well via conduit 22.

The pneumatic fluid weight device 31 and 31' is shown modified for useon the shaker box 17 and the suction tank 21 respectively.

As shown in-FlG. 2, the basic pneumatic fluid weight device of thisinvention consists of a pair of pneumatic tubes 32 and 33 connected inparallel relationship. The exit end of the pneumatic tubes 32 and 33 arespaced apart by a distance d which is exactly equal to 8.35 inches. Thetubes 32 and 33 communicate with conduits 34 and 34' respectively whichare connected to a source of compressed air 40 connecting air to theconduit at a pressure of approximately 3 psi. The low pressure is usedto maintain a constant flow of air through the tubes with a minimumamount of friction and the flow is maintained constant in each tube bymeans of flowmeters 35 and 35'. The air supply conduits 34 and 34communicate with the air supply source 40. A cap member has openings 29and 29' with adjusting sleeves 52 and 52 mounted therethrough. Theadjusting sleeves 52 and 52' are provided with adjusting screws 53 and53'. Tubes 32 and 33 extend upwardly into the adjusting sleeves 52 and52 respectively and are maintained in proper selected position by meansof adjusting screws 53 and 53. The inlet ends of the tubes 32 and 33 areconnected to the air supply lines 34 and 34' by suitable connectingmeans. As previously explained, the discharge ends of the pneumatictubes 32 and 33 are maintained apart a distance d which is exactly 8.35inches. Since a gallon of water weighs 8.35 pounds, a change of 1 poundper gallon in the drilling fluid is reflected in a differential pressureof one inch of water. This differential pressure is reflected on therecording device 41 which may be calibrated to record drilling fluidweight changes as inches of water which is directly equal to the weightchange in pounds of mud per gallon.

As shown in FIG. 3, the fluid weight device 31 is modified for use onthe shaker box 17. A housing 36 encloses the pneumatic tubes 32 and 33.The housing has an inlet opening 37 through its side for communicatingwith a source of drilling fluid such as the shaker box 17 as shown inFIG. 1. The housing is provided with an opening 38 at its bottom fordischarging drilling fluid from the inside of housing 36. The dischargeopening 38 is smaller than the inlet opening 37 in order to keep thehousing 36 full of drilling fluid. A water supply line 39, connected toa water'supply source (not shown) communicates with the outlet opening38 for use in cleaning the outlet opening.

As shown in FIG. 1, the fluid weight device 31 is connected to theoutside of shaker box 17 and communicates via an opening in the shakerwith the interior of shaker box 17 through the inlet opening 37 providedin the housing 36.

FIG. 4 discloses the fluid weight device 31 modified for use in thesuction tank 21. The apparatus is essentially the same as described withreference to FIG. 2 except that the housing 36 has been eliminated andfloat means 42 have been added. The tubes 32 and 33 are connected inparallel relation by means of the cap member 30 and adjusting sleeves 52and 52' as previously described. The housing 36 is replaced by a floatmeans 42 consisting of air chambers 43, 44, 45 and 46 which areconnected by means of suitable connecting rods 47, 47' and 48, 48' to aconnecting ring 49. The tubes 32 and 33 extend downwardly through thering 49 so that the cap member 30 rests inside the ring 49 and maintainsthe tubes 32 and 33 in vertical alignment. Tubes 32 and 33 are connectedto flexible conduits 51 and 51' which in turn communicate with airsupply conduits 34 and 34. The floating chambers 43, 44, 45 and 46 floaton the surface of the drilling fluid in the suction tank 21 and maintainthe tubes 32 and 33 at constant submersion depth regardless of changesin the depth of the drilling fluid in the tank 21. While it is notessential that the float means be anchored, I prefer to provide ananchor means consisting of a collar 56 connected to the ring 49 by meansof anchor bar 57. An L-shaped pivot rod 54 is connected at one end to aC-clamp 55. The C-clamp 55 connects the pivot rod 54 to the side of thetank 26. The collar 56 is positioned over the pivot rod 54 for anchoringthe fluid weight device in proper position in the tank while allowing itto rise and fall with the changing depth of drilling fluid. Theoperation of the device is exactly the same as previously described.

Having now described a preferred embodiment of my invention what I claimis:

1. An apparatus for weighing drilling fluid at a shaker box comprising apair of pneumatic tubes mounted in parallel relationship, each of saidtubes being open at one end and communicating with a source ofpressurized air at the other end said open end of one tube beingvertically spaced a pre-determined distance from the end of the othertube, control means for delivering and maintaining a constant and equalrate of air flow to each of said tubes, housing surrounding saidpneumatic tubes with an inlet opening in the side of said housing forreceiving said drilling fluid from an opening in the side of said shakerbox, discharge opening in the bottom of said housing, said dischargeopening being smaller than said inlet opening to maintain a level ofsaid drilling fluid in said-housing substantially equal to the level insaid shaker box, flow of said drilling fluid through said housing meansbeing over the open ends of said pneumatic tubes immersed in saiddrilling fluid.

2. The apparatus of claim 1 wherein said housing means includes a capmember having a pair of spaced openings therethrough, an adjustingsleeve is mounted over each of said openings and extend upwardly fromsaid cap member in parallel relationship, each of said pneumatic tubesextends through a respective one of said adjusting sleeves and saidspace openings and an adjusting screw extends through the wall of eachof said adjusting sleeves to frictionally engage said pneumatic tubesand maintain said tubes in position relative to each other with theirends vertically spaced apart a predetermined distance.

3. The apparatus of claim 2 wherein said predetermined distance is 8.35inches.

4. The apparatus of claim 1 wherein a water supply line communicateswith said housing adjacent the discharge opening to periodically cleansaid housing means.

5. An apparatus for weighing drilling fluid comprising a pair ofpneumatic tubes mounted in parallel relationship, each of said tubesbeing open at one end and communicating with a source of pressurized airat the other end, said open end of one tube being vertically spaced fromthe end of the other tube,

a cap member having a pair of spaced openings therethrough, an adjustingsleeve mounted over each of said openings and extending upwardly fromsaid cap member in parallel relationship, each of said pneumatic tubesextends through a respective one of said adjusting sleeves and saidspaced openings, an adjusting screw extending through the wall of eachof said adjusting sleeves to frictionally engage said pneumatic tubesand maintain said tubes in position relative to each other with theiropen ends vertically spaced apart a predetermined distance, I

float means connected to said pneumatic tubes, said float meanscomprising a plurality of air chambers surrounding said tubes, said airchambers being fastened around a connecting ring with said pneumatictubes extending vertically through said ring with said cap memberresting on top of said connecting ring and maintaining said pneumatictubes in vertical alignment.

6. The apparatus of claim 5 wherein an anchor means is connected to saidfloat means, said anchor means comprises an anchor rod connected at itsone end to said connecting ring and extending outwardly therefrom and acollar connected to the other end of said anchor rod.

1. An apparatus for weighing drilling fluid at a shaker box comprising apair of pneumatic tubes mounted in parallel relationship, each of saidtubes being open at one end and communicating with a source ofpressurized air at the other end said open end of one tube beingvertically spaced a predetermined distance from the end of the othertube, control means for delivering and maintaining a constant and equalrate of air flow to each of said tubes, housing surrounding saidpneumatic tubes with an inlet opening in the side of said housing forreceiving said drilling fluid from an opening in the side of said shakerbox, discharge opening in the bottom of said housing, said dischargeopening being smaller than said inlet opening to maintain a level ofsaid drilling fluid in said housing substantially equal to the level insaid shaker box, flow of said drilling fluid through said housing meansbeing over the open ends of said pneumatic tubes immersed in saiddrilling fluid.
 2. The apparatus of claim 1 wherein said housing meansincludes a cap member having a pair of spaced openings therethrough, anadjusting sleeve is mounted over each of said openings and extendupwardly from said cap member in parallel relationship, each of saidpneumatic tubes extends through a respective one of said adjustingsleeves and said space openings and an adjusting screw extends throughthe wall of each of said adjusting sleeves to frictionally engage saidpneumatic tubes and maintain said tubes in position relative to eachother with their ends vertically spaced apart a predetermined distance.3. The apparatus of claim 2 wherein said predetermined distance is 8.35inches.
 4. The apparatus of claim 1 wherein a water supply linecommunicates with said housing adjacent the discharge opening toperiodically clean said housing means.
 5. An apparatus for weighingdrilling fluid comprising a pair of pneumatic tubes mounted in parallelrelationship, each of said tubes being open at one end and communicatingwith a source of pressurized air at the other end, said open end of onetube being vertically spaced from the end of the other tube, a capmember having a pair of spaced openings therethrough, an adjustingsleeve mounted over each of said openings and extending upwardly fromsaid cap member in parallel relationship, each of said pneumatic tubesextends through a respective one of said adjusting sleeves and saidspaced openings, an adjusting screw extending through the wall of eachof said adjusting sleeves to frictionally engage said pneumatic tubesand maintain said tubes in position relative to each other with theiropen ends vertically spaced apart a predetermined distance, a floatmeans connected to said pneumatic tubes, said float means comprising aplurality of air chambers surrounding said tubes, said air chambersbeing fastened around a connecting ring with said pneumatic tubesextending vertically through said ring with said cap member resting ontop of said connecting ring and maintaining said pneumatic tubes invertical alignment.
 6. The apparatus of claim 5 wherein an anchor meansis connected to said float means, said anchor means comprises an anchorrod connected at its one end to said connecting ring and extendingoutwardly therefrom and a collar connected to the other end of saidanchor rod.